The present invention claims priority to the priority document, Japanese Patent Application No. P2000-391470 filed in Japan on Dec. 22, 2000, and incorporated by reference herein.
1. Field of the Invention
This invention relates to an adjusting method for cathode position of an electron gun and a electron gun for a cathode ray tube. More particularly, after a positional adjustment is executed for a position of an apex point of a cathode to become a center of a grid aperture of a first grid, an adjustment for a distance between the cathode and the first grid is independently executed, and accordingly even a cathode having a dome shaped surface can be fixed to a right position relative to the aperture of the first grid with higher precision.
2. Description of the Related Art
An electron gun of a cathode ray tube is so constructed, for example as shown in FIG. 9, as to be mechanically linked and supported with a predetermined positional relation mutually by fixing a cylindrical shaped first grid 11, a second grid 12, a third grid 13, a forth grid 14 and a fifth grid 15 to a beading glass 16, respectively.
Further a cylindrical cathode structure 30 is positioned within the first grid 11 and a cathode 31 is provided on a top surface of the cathode structure 30. In this case, when the cathode structure 30 is assembled within the first grid 11, a grid aperture 11h provided at the first grid 11 and the cathode structure 30 are adjusted to be coaxial and further, a gap between the first grid 11 and the cathode 31 to be a predetermined value (it is called as a dgk-value adjustment).
Further a test for improving focus characteristics has been done by employing a cathode having a dome shaped surface such as an impregnate type cathode, for example, and by minimizing a work area of a cathode due to concentration of an electronic field from a first grid.
In a case when the surface of the cathode 31 is formed to be dome shaped, a position of the apex point of the dome shaped cathode may have dispersion at every cathode.
When the grid aperture 11h and the cathode structure 30 are adjusted to be coaxial, it sometimes occurs that the position of the apex point and a center of the grid aperture 11h are not coincided due to such dispersion of the apex point the cathode 31.
When the position of the apex point and the center of the grid aperture 11h are not coincided, a track of a beam emitted from the cathode 31 is bent and it causes the problems that the shift amount of the spot formed on a phosphor screen of the cathode ray tube becomes large.
Further the surface of the cathode 31 is dome shaped, so that if it is not precisely adjusted for the gap between the apex point and the first grid 11 to be a predetermined space by properly detecting the position of the apex point of the cathode surface, the gap between the first grid 11 and the cathode 31 may have dispersion, and it causes a problem in which cut-off levels of R, G and B beams have dispersion due to such dispersion of the gaps.
According to the present invention, an adjusting method for a cathode position of an electron gun is presented capable of properly adjusting a position of a cathode, although an impregnate type cathode is employed as a cathode.
The adjusting method of the present invention includes: a step for supporting a cathode structure at a cathode holder; a step for detecting a position of an apex point of the cathode of the cathode structure supported by the cathode holder; a step for fixing the cathode holder to a first grid after executing a position adjustment for the position of the apex point of the cathode to be a center of a grid aperture of the first grid; and a step for fixing the cathode holder and the cathode structure after executing the position adjustment of the detected position of the apex point of the cathode and the first grid to be a predetermined value.
Further an electron gun of a cathode ray tube of the present invention comprises: a cathode colder; a cathode structure supported by the cathode holder; a cathode constituting the cathode structure; and a first grid having a grid aperture; wherein an apex point of the cathode is fixed to be positioned to a center of the grid aperture of the first grid.
According to the present invention, a cathode structure having a cathode with a dome shaped surface is mounted within a cathode holder. A position of the apex point of the cathode in the cathode structure supported by the cathode holder is detected and then the cathode holder is fixed to the first grid after a position adjustment where a position of an apex point of the cathode is coincided with a center of the grid aperture of the first grid. Further the cathode holder and the cathode structure are fixed after executing the position adjustment in which the gap between the detected position of the apex point of the cathode and the first grid becomes a predetermined value.